Surface micromachining process

Abstract

A method for making micromachined structures that includes pinpoint polysilicon bumps for eliminating the stiction problem associated with elements of the micromachined structure, such as movable or fixed beams. The pinpoint polysilicon bumps provide a reduced contact area for the beam which reduces the chances that there will be a stiction problem due to static or surface charge. The method takes advantage of an edge alignment technique to achieve a geometry for pinpoint bump structures of as low as 0.20 μm. The bump structures are located in a region of the movable and fixed beams at the edge adjacent the gaps between the interleaved fingers. The method forms bump structures that have a circular design. The formation of the bump structures is carefully controlled with respect to the overlap of these bump structures into interdigitated structures.

I claim: 
     
       1. A method for forming polysilicon pinpoint members on micromachined polysilicon structures, comprising the steps of: forming at least a first layer of material on a substrate;   forming a spacer layer of material on the first layer of material;   forming a pattern of holes in the spacer layer with each hole having a diameter and depth;   forming a microstructure polysilicon layer on the spacer layer such that microstructure polysilicon material fills the pattern of holes in the spacer layer;   forming a micromachined polysilicon structure from the microstructure polysilicon layer and removing the spacer layer to expose a pattern of polysilicon pinpoint members formed by the microstructure polysilicon material in the pattern of holes in the spacer layer.   
     
     
       2. The method as recited in claim 1, wherein the pattern of holes in the spacer material is formed by a mask. 
     
     
       3. The method as recited in claim 2, wherein the holes have a 1.6μ diameter. 
     
     
       4. The method as recited in claim 2, wherein the holes have a 2000 Å depth. 
     
     
       5. The method as recited in claim 1, wherein the micromachined polysilicon structure is formed by a mask. 
     
     
       6. The method as recited in claim 5, wherein the polysilicon pinpoint members are formed at edges of the micromachined polysilicon structure. 
     
     
       7. The method as recited in claim 6, wherein each of the polysilicon pinpoint members has a contact area beneath the micromachined polysilicon structure that ranges from substantially a point to approximately 0.201 μm 2 . 
     
     
       8. The method as recited in claim 5, wherein an overlap of edges of the micromachined polysilicon structure ranges from 0.20 μm to 0.45 μm.